A PCB Sensor for Status Monitoring of Stored Food Stocks

Cereal grains are important food stocks that can be safely stored for long periods of time if stored at an appropriate temperature and moisture content. As such, they are of considerable interest for long-duration manned space missions. However, if exposed to moisture, the grains will imbibe water and begin to germinate, spoil, or become contaminated by the propagation of various microorganisms, such as fungi. Imbibed moisture can be detected capacitively, since the relative permittivity of water is much higher than the relative permittivity of organic materials. Since grains such as corn kernels are relatively large compared to the size of traditional microsensors, a printed circuit board capacitive fringing field sensor was developed to detect the imbibed moisture in corn kernels through measuring the resulting increase in capacitance. Sets of corn seed of varying moisture content were obtained and evaluated with the sensor. The results were compared with measurements from a commercially available grain moisture content tester and demonstrated a linear increase in sensor capacitance as a function of kernel weight and moisture content.